1. Field of the Invention
The present invention relates to an image display apparatus for displaying data of a computer or a facsimile, and more particularly to an apparatus which forms and displays an image on a repetitively usable image carrier which carries an erasable image thereon.
2. Description of the Prior Art
A CRT display has been widely used a the image display apparatus for displaying data of the computer or facsimile. In such a CRT display, when an image is to be added to a displayed image, the additional information is input by a light pen, a digitizer or character keys. Since it requires means for converting the additional information to electrical signals and a large capacity memory, the apparatus is complex in construction and expensive. Further, when such additional image information input system is used, the types of image information which can be input are limited or a resolution of the input image is relatively low.
The assignee of the present application has proposed an image display apparatus which uses a moving belt-like image carrier to replace with the prior art image display apparatus. Such proposed apparatus is shown in FIG. 1, in which numeral 1 denotes a housing, numeral 2 denotes a display unit mounted in the housing 1, numeral 3 denotes a display window of the display unit 2, numeral 4 denotes a rigid transparent member such as acrylate plate or glass plate mounted on the display window 3, numeral 5 denotes a laser beam scanner, numeral 6 denotes an f-.theta. lens, numeral 7 denotes a reflection mirror, and numeral 8 denotes an endless belt-like photoconductor (or photosensitive belt) (hereinafter referred to as belt photoconductor) which is an image carrier guided in the housing 1 by guide rollers 9, 10, 11 and 12 and intermittently driven by drive means (not shown) which is coupled to at least one of guide roller shafts.
An output light from a semiconductor laser (not shown) which is modulated by an image electrical signal is scanned in one direction by the scanner 5 and illuminates a back side of the belt photoconductor 8 through the f-.theta. lens 6 and the mirror 7. The photoconductor 8 may comprise a photoconductive layer formed on a transparent and conductive substrate.
A developing unit 15 including a sleeve 17 having a toner carrying magnet 16 rotating in a direction of an arrow mounted therein is arranged to face a surface of the belt photoconductor 8 at an exposure position A, and conductive and magnetic developers (toners) 18 supplied onto the sleeve surface contact to the photoconductor surface while they are uniformly regulated by a blade 19. A D.C. voltage from a D.C. power supply (see FIGS. 2 and 3) is applied across the sleeve 17 of the developing unit 15 and the substrate of the photoconductor 8. Rollers 13 and 14 ar arranged in the vicinity of the exposure/develop position so that the belt photoconductor 8 is kept planar and a distance between the photoconductor surface and the sleeve 17 of the developing unit 15 is precisely kept constant. In this manner, the toner image written on the surface of the belt photoconductor 8 by the beam irradiation at the position A facing the developing unit 15 is transferred to the display unit 2.
The display unit 2 has the rectangular window 3 formed on the front side of the housing 1 so that the toner image on the photoconductor can be externally viewed through the transparent member 4 which covers the window 3. The photoconductor 8 is automatically or manually stopped for a desired time period when a desired visible image area comes under the window 3. Thus, the stationary toner image on the photoconductor can be viewed through the window 3 and the transparent member 4.
Numeral 20 denotes a lamp for erasing hysteresis on the photoconductor 8. It is mounted downstream of the exposure position A to face the back side of the photoconductor 8. It is turned on while the belt photoconductor 8 is moved, and turned off when it is stopped. Numeral 21 denotes a console arranged on the housing 1 below the display unit 2 to instruct various operations. It includes a plurality of buttons to instruct the movement and the stop of the photoconductor 8.
FIGS. 2 and 3 illustrate a principle of image formation on the belt photoconductor 8 of the apparatus of FIG. 1.
FIG. 2 shows charges in a light area of the information light (laser beam) LB. When the toners 18 having the D.C. voltage applied thereto through the sleeve 17 contact to the photoconductor 8, an electric field is applied to the transparent conductive layer 8b of the photoconductor 8. If the information light transmitted through the transparent substrate (for example polyethylene telepthate film) 8a is irradiated to the conductive layer 8b, photo-carriers e are created in the photoconductive layer 8c and are guided to the vicinity of the surface of the photoconductive layer 8c under the action of the electric field. As a result, a strong electrostatic attractive force acts between the conductive and magnetic toners 18 and the photoconductive layer 8c so that the toners 18 are deposited on the photoconductive layer 8c or the photoconductor 8.
In the illustrated example, the photoconductive layer 8c is an N-type semiconductor and a positive voltage is applied to the toners 18 so that the negative carries e created in the vicinity of the substrate 8a in the photoconductive layer 8c by the irradiation of the information light LB are guided toward the surface of the photoconductive layer 8c. As a result, a strong electrostatic attractive force acts between the positive toners 18 and the photoconductor 8 and the toners 18 are deposited to the photoconductor 8.
FIG. 3 illustrates charges in a dark area. The electrostrictive force acts between the toners 18 and the transparent conductive layer 8b by the electric field applied therebetween but the force is small because of a long distance therebetween and the presence of the photoconductive layer 8c therebetween. Accordingly, the toners 18 are removed from the surface of the photoconductive layer 8c or the photoconductor 8 by the magnetic force of the rotating magnet 16 arranged in the stationary sleeve 17 and the deposition force among the magnetic toners 18.
A new image can be formed on the photoconductor 8 by passing the toner image through the exposure position A. When the toner holding area on the photoconductor 8 changes to the toner non-holding area, the electrostatic attractive force of the toners 18 reduces and the toners 18 are removed by the magnetic field of the magnet 16 and a light area without toner deposition is created. The developing unit 15 also serves as cleaning means. On the other hand, when the toners are to be retained, the carriers e are again injected by the information light LB and the toners 18 are attracted against the magnetic field of the rotating magnet 16 so that the toners 18 are retained. Accordingly, the toner image on the photoconductor surface does not adversely affect to the formation of the next image and hence no separate cleaning means is required.
In another system in which the endless belt-like image carrier is intermittently moved to form and display the image, a thermo-sensitive record medium made of Ag.sub.2 HgI.sub.4 which is a compound of silver, mercury and iodine is used as the belt and a thermal recording head is used as the image forming means.
In the image display apparatus of the type described above, when a new image is to be added to the existing toner image, the toner image must be additionally formed on the belt photoconductor. However, in the above process, it is not possible to add the information without erasing the existing toner image. In the above display system, it is necessary to convert the additional information to an electrical signal in order to form the additional information on the photoconductor. This leads to the complexity of the construction of the apparatus as it is in the CRT display system.
In the above image display apparatus, the input image information signal is stored in an information storage medium such as an optical disc or a memory in a form of electrical signal. In order to additionally input the image signal to such electrical signal image information, it is necessary to visualize the electrical signal image information by the image display apparatus to allow visual observation by an operator, input the additional image information by some means and convert it to an electrical signal and transfer it to the information recording medium or the memory.
In the image display apparatus shown in FIG. 1, there is no means for additionally inputting the image information nor means for converting the additional input image to an electrical signal.